A number of synthetic thermoplastic polymers are employed in the production of surgical filaments such as sutures and ligatures. Such polymers include nylon, polyester, and polypropylene. In the preferred form, a surgical filament is employed in the form of a monofilament, if that is possible, because monofilaments are easy to draw through tissue and have lower tissue reaction than do braided filaments. However, many of the synthetic thermoplastic polymers that are employed as surgical filaments are too stiff or non-compliant to be used in the form of monofilaments.
Polypropylene is the leading synthetic thermoplastic polymer that is employed in the form of a monofilament surgical suture. However, the properties of polypropylene are such that, especially with the larger sizes such as 2/0 and higher, the compliance is just adequate for the suture to be employed in the form of a monofilment. Thus, there has been an extensive search for a synthetic thermoplastic polymer that is strong, but yet is quite compliant so that it can readily be employed in the form of a monofilament.
One solution to this problem is proposed in U.S. Pat. No. 4,224,946, which describes a monofilament suture composed of a polyether-polyester block copolymer. For instance, a preferred version is a polyalkylene terephthalate block alternating with a polyoxytetramethylene block. An earlier proposed solution for the problem of low compliance with monofilament sutures was made in U.S. Pat. No. 3,454,011, in which it was proposed to use Spandex polyurethane block copolymers as monofilament surgical sutures. A typical Spandex polyurethane block copolymer contains a urethane block alternating with a block of polyoxytetramethylene ether. However, it was found that such sutures were too elastic, and therefore, did not find general acceptance in the medical profession.
Thus, the prior art is aware of at least two types of block copolymers that employ polyoxytetramethylene ether blocks alternating with other types of blocks, which were proposed as flexible monofilament surgical filaments. In the case wherein the polyether blocks alternated with polyurethane blocks, the sutures were too elastic and have not been commercially successful. In the case of the block copolymers wherein the polyether blocks alternated with polyester blocks, the technology is too new to determine whether or not such sutures will find general acceptance. Therefore, we have the situation where one type of block copolymer containing a polyether block was found not to be acceptable as a surgical suture, and another type of block copolymer containing a similar polyether block wherein it does not appear that such block copolymers will make acceptable surgical sutures; although it is too soon to give an assessment of the commercial acceptability of such sutures.
This invention relates to surgical filaments made from a block copolyetheramide wherein the filaments are quite strong, and yet are highly compliant, and therefore appear to be an excellent solution to the desire in the profession for having a monofilament suture that is both strong and compliant.